Wax deposition at the inner wall of oil pipelines is a severe problem in today's oil production infrastructure. When warm oil flows through a pipeline with cold walls, wax will precipitate and adhere to the walls. This in turn will reduce the pipeline's cross-sectional area, which without counter measures will lead to a loss of pressure and ultimately to a complete blockage of the pipeline.
To know when remediation techniques (e.g. pigging, heating, etc.) have to be applied, it is essential to know the current thickness of the wax layer. Known techniques for determining or measuring the current wax layer's thickness include the use of pipeline inspection gauges (pigs), pressure pulse techniques, and pressure drop measurement (over the complete pipeline). However, each of these known techniques has several drawbacks. For instance, pigs and pressure pulse techniques give no continuous measurement, they may disturb operation procedures, and they are expensive. A pressure drop measurement approach gives only an integral measurement over the whole pipe length, and the measured pressure drop is influenced by a number of parameters in addition to wax thickness (e.g. the roughness of the inside of the pipeline), so there is really no direct correlation to wax thickness.